# The metric system and estimation

2011-10-17

Perhaps the best thing about the metric system (more formally, the International System of Units) is the way in which it allows for the easy estimation of many practical problems, and takes advantage of the intuitive connections people can make.

For instance, one millilitre (mL) of volume occupies a space of 1 centimetre (cm) by 1 cm by 1 cm. It is easy to imagine a cube that is 1 cm to a side, so it is easy to imagine what 1 mL of liquid would look like. Similarly, knowing that 1 litre (L) of water (a very familiar quantity of matter) has a mass of 1 kilogram (kg) allows a person to pretty easily consider what the weight of something in kilograms might be. A volume of 1000 L of water weighs one metric tonne, and occupies a space of one cubic metre.

The metric connections extend to other elements of science and everyday life. The metric temperature scale is well suited to a planet where water is exceptionally important. While calories are not strictly a metric unit, they do tie usefully into the common theme of water, with one calorie being the amount of energy required to heat 1 cubic centimetre (equivalent to 1 gram, and to 1 mL) of water by 1˚C. Note that ‘calories’ as expressed in relation to food are usually kilocalories: the amount of energy required to heat 1 L of water by 1˚C.

All very useful!

{ 2 comments… read them below or add one }

. October 18, 2011 at 11:22 pm

To start with, the way Fahrenheit makes his thermometer is nothing new.

You just melt the end of a glass rod with a hole down the middle and then blow down the hole to make the molten bulb on the end expand into what will become the thermometer bulb that contains the mercury.

Getting the mercury into the bulb is really nifty. Watch. You put the hot rod bulb up into the mercury and the vacuum you made in there with the heat sucks the mercury up into the bulb.

OK. Now for the absolutely lunatic way Fahrenheit comes up with the Fahrenheit scale, so hang in there.

He starts with a scale, the bottom end of which is going to be the temperature of frozen ice, zero. He calls boiling water 60. 1/8 and 3/8 of the scale are freezing water and the temperature of a healthy armpit. Are you still with me? OK. Make each degree four degrees, which turns freezing water from 7 1/2 to 30 and a healthy armpit to 90, but doesn’t divide by 8.

So, make 30 32, and 90 96 and and there you are, plus one last tweak.

Clear as mud? I never said what Fahrenheit did would make any sense.

Milan October 18, 2011 at 11:24 pm

That little clip is from James Burke’s Connections, which was discussed here before.

You can see the whole episode on YouTube – just search for Connections³, Episode 10 : “In Touch”.

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